The invention relates in general to an antenna device and in particular to an antenna device with improved reception.
Embedded antennas, such as chip antennas and planar antennas, are widely applied to wireless communication devices. One conventional chip antenna is a ceramic chip antenna produced by LTCC (Low Temperature Co-fired Ceramic) technology. Conventional planar antennas such as microstrip antennas, printed antennas and Planar Inverted F Antennas (PIFAs), are generally applied in GSM, DCS, UMTS, WLAN and bluetooth wireless equipment such as mobile phones and wireless LAN adapters.
Referring to FIGS. 1a and 1b, a conventional wireless communication device 10 with PIFA, such as a wireless LAN adapter, primarily comprises a plastic housing C and a printed circuit board 20 disposed therein. The housing C encloses the printed circuit board 20 with PIFA structure formed thereon for transmitting and receiving radio signals. As shown in FIG. 1b, the printed circuit board 20 features a conventional PIFA structure, comprising a substrate 200, a feed line 201, a short line 202, a longitudinal wire 203 and a ground G. The longitudinal wire 203 has an open end 2030 and a closed end 2031 connecting the short line 202. In FIG. 1b, the short line 202 connects the closed end 2031 with the ground G, and the feed line 201 is extended from the middle part of the longitudinal wire 203 to an external circuit (not shown). Particularly, the feed line 201 and the ground G are insulated, and the distance from the open end 2030 to the closed end 2031 is substantially equal to ¼ of a radio signal wavelength. As the PIFA structure including the feed line 201, short line 202, longitudinal wire 203 and ground G is formed on the substrate 200 surface, however, it is suitable for horizontally polarized radio waves but not preferable for receiving vertically polarized radio signals.